The high cycle fatigue strength of porous coated Ti‐6Al‐4V is approximately 75% less than the fatigue strength of uncoated Ti‐6Al‐4V. This study separates the effects of three parameters thought to be responsible for this reduction: interfacial geometry, microstructure, and surface alternations brought about by sintering. To achieve the goal of one parameter variations, hydrogen‐alloying treatments, which refined the lamellar microstructure of β‐annealed and porous coated Ti‐6Al‐4V, were formulated. The fatigue strength of smooth‐surfaced Ti‐6Al‐4V subjected to hydrogen‐alloying treatments is 643–669 MPa, significantly greater than the fatigue strength of β‐annealed Ti‐6Al‐4V (497 MPa) and also greater than the fatigue strength of preannealed, equiaxed Ti‐6Al‐4V (590 MPa). The fatigue strength of porous coated Ti‐6Al‐4V, however, is independent of microstructure. This leads to the conclusion that the notch effect of the surface porosity does not allow the material to take advantage of the superior fatigue crack initation resistance of a refined α‐grain size. Thus, sinternecks act as initiated microcracks and fatigue of porous coated Ti‐6Al‐4V is propagation controlled. Copyright © 1990 John Wiley & Sons, Inc.
